Process for the electrodeposition of a decorative corrosion resistant nickel-chromium coating and products thereof



United States Patent PROCESS FOR THE ELECTRODEPOSITION OF A DECORATIVE CORROSION RESISTANT NICKEL-CHROMIUM COATING AND PROD- UCTS THEREOF Adolf E. Schwedhelm, Wiener Strasse 42, and Friedrich Karl Kiill, Lercllenstrasse 44, both of Solingen, Germany N0 Drawing. Filed Dec. 7, 1964, Ser. No. 416,606

Claims priority, application Germany, Dec. 24, 1963,

. K 51,724 2 Claims. (Cl. 29-194) This invention relates to a process for producing highly corrosive resistant nickel deposits using electrophoresis action in an electroplating process to codeposit a layer of nickel containing finely-divided electrically conductive particles uniformly dispersed therein. More particularly, it relates to a process for producing decorative and highly corrosion resistant nickel-chromium deposits which consist of a basic layer of nickel deposits containing uniformly dispersed and finely-divided electrically conductive particles and a thin outer layer of chromium.

Nickel, because of its corrosion resistant properties, is used extensively in the form of plating to protect other and more vulnerable materials from atmospheric corrosion. For decorative purposes, nickel deposits are frequently used for corrosion resistance and the thin covering of chromium provides additional tarnish resistance. However, the decorative covering of chromium adds little to the protective value of the nickel plating when the customarily very thin chromium deposits are used. The corrosion of the resultant nickel-chromium coating generally proceeds at pores in the coating. These pores may exist originally because of imperfections in the electroplating process; the coating may be too thin, or the pores may develop as a result of local corrosion of the metallic coating itself. In any event, the corrosion causes the basic metal to suffer accelerated galvanic corrosion at the base of the pore, because of its small anodic area and the large cathodic area of the protective coating.

Attempts have been made to increase the corrosion resistance of the nickel-chromium coating without increasing the coating thickness. Among them, the incorporation of fine nonelectrically conducting particles such as aluminum oxides, titanium oxide, and other ceramic materials into the basic nickel layer has met with some success. Apparently, the fine nonconductive particles dispersed in the nickel deposits serve to spread the corrosion sites uniformly on the coated surface which, in effect, lessen the local attack on one or more of the pores. The net effect of dispersing nonconductive particles in the basic layer is to lengthen the service life of the nickel-chromium coating. Their presence in the coating, however, does not effectively alter the electrochemical process of the corrosion. Therefore, they do not actually increase the corrosion resistance of the coating.

We have now found that the corrosion resistance of nickel deposits, particularly that of the nickel-chromium coating, can be substantially increased using nickel deposits prepared according to the process of this invention. Broadly stated, the process comprises electrodepositing nickel from an aqueous solution of at least one nickel salt in which there is dispersed electrically conductive particles having a particle size ranging from 20 to 100 A. (angstroms). The amount of electrically conductive particles dispersed in the nickel plating bath can be varied Within a wide range and still produce the beneficial result. We have found that the optimum result is obtained using a concentration of about 0.5 to about 2 grams of electrically conductive particles per liter of nickel bath. Among the electrically conductive particles that can be used in the present invention, we find carbon powders having a particle size in the range stated above to be eminently suitable.

For decorative purposes, a thin layer of chromium deposits is preferably used as an outer coating to provide the brilliancy and tarnish resistance. These chromium deposits can be plated onto the supporting layer of nickel from any suitable chromium bath. The resultant nickelchromium coating exhibits exceptionally high corrosion resistance. The superior corrosion resistance of this coating is further confirmed by a comparative Corrodkote Test (a standard accelerated corrosion test for nickelchromium coating) comparing nickel-chromium coatings containing aluminum oxides, titanium dioxides, and ceramic powder having a particle size ranging from 0.2 to 0.6 microns in the nickel deposits with the coating of this invention.

The substantial increase in the corrosion resistance of the nickel-chromium coating of this invention is due to the fine electrically conductive particles incorporated into the nickel deposits. Investigation indicates that the electrically conductive particles act as depolarizers for the chromium which eflfectively change the electrochemical performance of the composite coating. As a result, the corrosion resistance of the nickel-chromium coating is greatly increased.

Further to illustrate this invention, specific examples are described hereinbelow:

EXAMPLE 1 A nickel plating bath was prepared which has the following composition and physical characteristics:

250 g./l. nickel sulfate (NiSO 6H O) 40 g./l. boric acid (H BO 10 g./l. nickel chloride (NiCl -6H O) 0.01-30 g./l. carbon (particle size 20-100 angstroms) 0.25 g./l. Z-butyne, l-4 dial 6.0 g./l. m-benzene disulfonic acid sodium salt 0.2 g./l. surfactant Temperature: 50-55 C.

Agitation: Agitation by air or cathode movement 0.5 to 2 grams per liter of carbon powder having a particle size ranging from 20 to A. was added to the bath and thoroughly mixed. A current density of 2 to 6 amp./dm. was used for the plating operation. A decorative chromium coating of about 0.3 micron thickness was plated on the resultant nickel deposits which contained carbon particles uniformly dispersed therein. The chromium bath used is the Well-known type containing chromic and sulfuric acids in their optimum concentrations. The nickel-chromium coating obtained was subjected to Corrodkote Test and was found to be far superior to a standard nickel-chromium coating of equal thickness.

EXAMPLES 2-3 The following baths were prepared:

Example 2 300 g./l. nickel sulfate (NiSO .6H O) 40 g./l. boric acid (H BO 40 g./l. nickel chloride (NiCl .6H O) 0.01-30 g./l. carbon (particle size 20-100 angstroms) 0.2 g./l. heXadiyne-Z, 4-diol-l,6

2.0 g./l. o-benzaldehyde sulfonic acid sodium salt 0.2 g./l. surfactant Temperature: 50-55 C.

Agitation: Agitation by air or cathode movement Example 3- 80 g./l. nickel fluoborate 25 g./l. nickel chloride (NiCl .6H O) 40 g./l. boric acid (H BO 0.01-30 g./l. carbon (particle size 20-100 angstroms) 0.2 g./l. Z-butyne, l-4 diol 0.05 g./l. heXadiyne-Z, 4-diol-1,6

2.0 g./l. o-toluene sulfonamide 2.0 g./l. o-benzaldehyde sulionic acid sodium salt 0.2 g./l. surfactant Temperature: 5055 C.

Agitation: Agitation by air or cathode movement To these baths, 0.5 to 2 grams of carbon per liter of solution were added. Nickel deposits were plated from these baths similar to Example 1 using a current density in the range of 2 to 6 amp. per dm. Subsequent to the nickel deposition, about 0.3 micron chromium deposits were plated thereon from a conventional chromium bath containing chromic acid, sulfuric and fiuosilicic acids in the optimum concentrations. The carbon particles used have a particle size range from 20 to 100 A. The resultant coatings were found to have excellent corrosion resistance in Corrodkote Tests.

Similar tests were made using conventional nickel sulfamate and nickel sulfate baths containing 0.2 g./l. hexadiynediol and 2 g./1. o-benzaldehyde sodium sulfonate. Equally good results were obtained from the nickel chromium coatings. In place of o-benzaldehyde sodium sulfonate, otoluene sul-fonamide or saccharin can be used. It was found that individual baths and additives have no eflFect on the corrosion resistance of the final coating. It is understood that plating baths suitable for the present invention must be capable of providing acceptable nickel 3 deposits.

It is noted that in the customary method of purifying nickel baths with activated carbon with a particle size on the average of microns, this carbon must be removed prior to the electroplating process. The large particle size of the activated carbon leads to rough, nodular and unsatisfactory nickel deposits. No increase of corrosion resistance can be obtained using carbon particles of this larger particle size.

We claim:

1. A metal article having thereon a corrosion resistant coating which comprises a coating of electrodeposited nickel containing uniformly dispersed, finely divided carbon particles of a size on the order of 20 to A., and an outer coating of electrodeposited chromium on said nickel.

2. The process of producing a corrosion resistant coating on a base metal, comprising electrodepositing nickel upon said base metal acting as a cathode from an aqueous solution containing at least one nickel salt and dispersed carbon particles of a size on the order of 20 to 100 A. in the amount of approximately 0.5 to 2.0 grams per liter, and electrodepositing chromium to form a layer on said nickel.

References Cited UNITED STATES PATENTS 2,999,798 9/1961 Eitel 204-41 X 3,057,048 10/1962 Hirakis 204-49 X 3,061,525 10/ 1962 Grazen 2049 3,152,971 10/1964 Tomaszewski et al. 204-41 3,152,972 10/1964 Brown et al 20441 3,152,973 10/1964 Tomaszewski et al. 2044l FOREIGN PATENTS 957,677 2/1957 Germany.

JOHN H. MACK, Primary Examiner. HOWARD S. WILLIAMS, Examiner.

G. KAPLAN, Assistant Examiner. 

1. A METAL ARTICLE HAVING THEREON A CORROSION RESISTANT COATING WHICH COMPRISES A COATING OF ELECTRODEPOSITED NICKEL CONTAINING UNIFORMLY DISPERSED, FINELY DIVIDED CARBON PARTICLES OF A SIZE ON THE ORDER OF 20 TO 100 A., AND AN OUTER COATING OF ELECTRODEPOSITED CHROMIUM ON SAID NICKEL.
 2. THE PROCESS OF PRODUCING A CORROSION RESISTANT COATING ON A BASE METAL, COMPRISING ELECTTODEPOSITING NICKEL UPON SAID BASE METAL ACTING AS A CATHODE FROM AN AQUEOUS SOLUTION CONTAINING AT LEAST ONE NICKEL SALT AND DISPERSED CARBON PARTICLES OF A SIZE ON THE ORDER OF 20 TO 100 A. IN THE AMOUNT OF APPROXIMATELY 0.5 TO 2.0 GRAMS PER LITER, AND ELECTRODEPOSITING CHROMIUM TO FORM A LAYER ON SAID NICKEL. 